Circuit interrupter



Aug. 19, 1941.

Filed April 26, 1939 O. MLLER CIRCUIT INTERRUPTER fw WM Aug. 19, 1941. l o. MULLER 2,253,390

CIRCUIT INTERRUPTER Filed April 26, 1959 2 sheets-sheet 2 WITNESSES:

` INVENToR 9,4% Ot 0 /Vu//ef interruptor.

UNITED STATE f '2,253,390 FICE 2.25am CIRCUIT INTERBUPTEB Otto Mller, Berlin-Siemensetadt, Germany, as-

eignor to Westinghouse Electric Mannheturing-'Company, East. Pittsburgh, Pa., a corporation o! Pennsyl Application April 26,

In Germany Claims.

The invention relates to electrical circuit interrupters in general, and more particularly uto circuit interrupters of the type having one or more current responsive thermal control elements operable in response to 4predetermined conditions to cause automatic opening of the An object oi the invention is the provision of an improved circuit interrupter of the type described with a novel means ior compensating the device for changes in ambienttemperature.

Another object of the invention is the provision of an improved circuit interrupter embodying a train ofv elements operable by one or more current responsive bimetai control elements to cause automatic opening or' the interrupter, and a single thermal element arranged in the chain of elements to compensate the device forchanges in ambient temperature.

Another object of the invention is the provision of an improved multi-pole circuit interrupter embodying a plurality of current responsive bi- `metal control elements, each operable to cause automatic opening of the interrupter in response to predetermined conditions, and a/,single ther- 1939. serial'No. 270,214 April zo, 193s (Cl. o-113) as in response to changes in ambient temperar'nanner that they maintain their equilibrium with reference to their common rotation point or points.

A particularly simple and advantageous arrangement results if the ambient temperature compensating element isconstructed as a double arm lever between the common slidable trip bar and the tripping contact or releasable element,

and the lever pivoted at the common center of gravity of the movable elements.

For the purpose of nullifying the eiiect of the acceleration forces named in part (2) above,

. the ambient temperature compensating element is, in accordance with a further aspect of 4the invention. mounted on an additional inertia body or mass which is rotatably mounted at its center or gravity. A pre-tensioned. spring is mounted ori this body and engaged by one end However, when the trip bar is moved by vibrations or jars, this quick movement is taken up by the flexing oi' the pre-tensioned spring and -tne inertia body remains stationary so that the vibrations or jars will not cause tripping or release of the interrupter.

The novel features that are considered characteristic of the invention are set forth in particulai.` in the appended claims. The invention itself, however, both as to structure and operation together with additional objects and advantages thereof will be best understood from the ioiiowing detailed description of several embodiments thereof when read in conjunction with the accompanying drawings, in which:

Figure 1 is a partly schematic view of the circuit interrupter ofthe invention, the thermal control unit being shown in front plan, and the circuit, main contacts and operating means for the main contacts being shown schematically;

Fig. 2 is a fragmentary front plan view of a modified embodiment of the invention;

Fig. 3 is a fragmentary front plan view of ra further 'modification of the invention embodying an additional inertia body and a prev-tensioned spring; and

Fig. 4 is a schematic view of another modification of the invention.

Referring to Figure 1 of the drawings, the circuit interrupter comprises in general a plurality of sets of main contacts 5, one set for each pole of the interrupter, a common electromagnetic operating and holding-means I for the contacts 5, and a thermal control or release device indicated generally at 9. which is operable in response to predetermined current conditions in the circuit oi any of the poles of the interrupter to cause automatic opening of the interrupter.

The main contacts 5 and their common electromagnetic operatingI means l may be of any conmaintained in closed circuit position by energization of the electromagnetic means 1., Upon deenergization of the electromagnetic means, the

contacts 5 are actuated to open circuit position l release device 9 contains a. pair o! contacts to be hereinafter described which are connected in series in the control circuitil1. These contacts are normally closed and are adapted to be opened in response to predetermined abnormal current conditions in any one o! the lines I9 to effect deenergization of the electromagnetic operating means 1, and consequently opening of the contacts 5 of the interrupter.

The thermal control device 9 comprises a base or casing 2 I, preferably oi.' molded insulating material, which is divided into a plurality of compartments 23, 25, 21 and 29 by partitions 3I formed integral with the casing. Suitable openings are provided in the walls oi the casing 2I to accommodate the various conductors which enter the casing.

A plurality of current responsive thermal control elements 33, one for each ypole of the interrupter, are `mounted one in each of the upper "compartments 23, 25 and 21 of the casing 2|.

The construction, mounting, and connection o! each oi the control elements 33 is identical so that a description oi one will suiilce.

Each of the thermal control elements is composed of a strip of bimetallic material and is rigidly secured at one end to an outwardly projecting bracket of an adjusting lever 35. 'I'he adjusting lever 35 is of conducting material and is pivotally mounted at one end on a terminal 31 by means of a screw 39. The screw 39 maintains the adjusting lever in good electrical contact with the terminal 31 and also serves as a pivot for the lever.

The i'ree end of the adjusting lever is bifurcated and engages the/,opposite sides of an eccentrically rotatable/adjusting member 4I. Rotation Vofthe adjusting member causes movement of the adjusting lever 35 about its pivot tov l to the current ilowing in the corresponding pole oi the interrupter. The insulating sleeve 43 ,serves to electrically insulate the windings of the heater coil 45 from the bimetallic strip 33. One end of the heating coil is electrically connected to the free end of the bimetallic strip 33 and the other end ot the heating coil is electrically connected to a terminal 41.

The two terminals 31 and 41 of each of the bimetallic control elements and their heating coils are electrically connected respectively in the corresponding main circuits I9, so that each bimetal control element is heated in response to the current ilowing through its corresponding main circuit I9. A

The electrical circuit through each pole of the interrupter extends from the left-hand terminal 31 through the bimetallic strip 33, back through the heating coil 45 to the opposite terminal 41 and through the main contacts 5 to the circuit I9. vEach of the bimetallic strips 33 is adapted to be deflected downwardly when heated in response to predetermined current conditions to cause automatic opening oi the interrupter by actuating a common insulating bar 49. 'I'he common trip bar 49 is guided for vertical move ment in a casing 2| by guides 5I formed in the partitions 3|. The trip bar 49 is provided with a plurality of spaced projections 53 rigidly secured to the bar, one for each of the bimetal strips 33. When any one oi' the bimetallic stripe 33 is deilected downwardly a predetermined amount in response to predetermined current conditions, the free end oi the bimetallic strip engages the corresponding projection 53 on the common bar 49 and causes downward movement of the 'bar 49 to effect automatic opening of the circuit interrupter.

In order to render the automatic operation of the thermal control device 9 independent of ambient temperature conditions, an ambient temf perature compensating element 55 is provided in the trainof movable elements taking part in the automatic operation of the device. The ambient temperature compensating element 55 comprises a double arm lever of bimetallic material which is pivotaliy supported intermediate its ends on a pivot pin 51. One end of the ambient temperature compensating element 55 is engaged by the lower end of the vertically movable common trip bar 49, and the opposite end of the ambient temperature compensating element 55 carries a movable contact 59 which normally engages a cooperating stationary contact II carried by a terminal strip 53. The ambient temperature compensating element 55 is biased in a counter-clockwise direction about its pivot 51 by means of a helical compression springs 55 interposed between the contact carrying end o! the element 55 and a portion of the casing 2|. The biasing spring 65 serves to normally mainl tain the movable contact 59 in engagement with the stationary contact 3|.

The contacts 59 and 5I are electrically connected in series with the winding o! the electromagnetic operating and holding means 1 in the control circuit I1, so that these contacts, when in closed position, serve to maintain the electromagnetic means 1 energized as long as the control circuit I1 is energized.

When any one of the bimetallic strips 33 is deflected downwardlyy in response to predetermined abnormal current conditions, the common bar 49 is moved downwardly thereby causing clockwise rotation ci the ambient temperature compensating element 55 about its pivot 51 to effect opening-of the contacts 59 and 5I against the biasing action of the spring 35. Opening of the contacts 59 and 5I causes deenergization of the electromagnetic means 1, eiecting simultaneous actuation o! the main contacts 5 oi' the interrupter to open circuit position.

Opening of the contacts 5 interrupts the main circuit I9, deenergizing the thermal control elements 33, thus'allowing them to cool. As soon as the deflected bimetallic control element 33 to the common pivot axis 51. This is attained by having the common pivot 51 of the movable has cooled a predetermined amount, it returns reclose upon energization of the control circuit The ambient temperature compensating .ele-

ment 55 functions to compensate the device for changes in ambient temperature in the following manner. The left-hand end of the ambient temperature compensating element is maintained in the position shown in Fig. 1 by the biasing action of the spring 65. Any changes in ambient tem-v perature 'causes the ambient temperature compensating element 55 to flex ytownward in response to a rise in ambient temperaturewand upward in response to a decrease in ambient temperature, free end of the ambient temperature compensating element 55 shifts the position of the com- This defiecting movement of the mony bar 43 in a corresponding direction changing a the position of the projections 53, so that greater or less deflecting movement of the bimetallic control elements isrequired to effect automatic operation of the control device 3.

The pivot pin 51, which supports the ambient temperature compensating element 55, is carried by a free end of an adjusting lever 51 which is' pivotally mounted about a fixed point 63, and disposed in a recess 1I in the back wall of the casing 2|. The free end of the adjusting lever 51 is notched Ias indicated at 13` and is adapted to be moved up or .down by an eccentric adjusting screw (not shown) to shift the position of the pivot pin 51 up or down. This construction and mounting arrangement provides a means for effecting simultaneous adjustment of the current-operating characteristics of all of the bimetallic control elements 33 within a given range. The adjusting lever 61 may be moved up or down to correspondingly shift the' position of the pivot 51, this changes the original position of the common lbar 43 and its projections 53 so that more or less deflecting movement of any of the'bimetallic control elements 33 is required to cause automatic opening of the interrupter, y The stationary contact 5I is electrically connected by the conducting strip 63 to a terminal 14, and the movable contact 53 is electrically connected to a terminal 15 through the agency of the vpivot 51 and lever 61 which are of conducting material, and through a conducting strip 11 which is rconnected to the terminal 15 at one end' and which engages the pivot end of the lever .61 at its other end. If desired, a suitable flexible. A shunt conductor may be provided for electrically connecting themovable contact 53 ducting strip 11.

In order to prevent the train of movable elements comprising the common bar 43, the ambient temperature compensating element 55 and the movable contact 53 'from being moved to cause false automatic opening of the interrupter, by vibrations or jars, the entire train of moving elements is statically balanced with respect to the common pivot or rotational point 51 of such train so that the acceleration forces produced by vibrations or jars are distributedover all of these elements in such amanner thatv the acceleration forces are in equilibrium with respect train of elements 43, 55, 53 located at the common center of gravity of this trainv of movable elements.

' The elements 43, 55, 53 and any parts carried thereby are 'constructed-and arranged so that the masses on either side of the commonpivot 51 are vbalanced with respect to this common pivot. secured to the ambient temperature compensating element 55 for the purpose of statically balancing the entire train of movable elements with respect to the pivot 51.

With

tions or jars applied to the interrupter will not cause movement of the train of elements 43, 55, 53 due to the fact that the acceleration forces lproduced on these elements by vibrations or jars,

are in equilibrium with reference to the common pivot 51 of the train of elements.

Static. balancing of the train of movable elements taking part in the automatic operation of' the breaker may also be attained with reference to a plurality of common'pivot or rotational t points by having the lcommon trip bar and the ambient temperature compensating element arranged as,a part of a movable parallelogram,

the joints or corners of which are formed by hinges.

The connecting bars of the parallelogram which are hingedly connected to the common bar may be supported on fixed or adjustable pivot points. 'Ihis construction is illustrated schematically 'in Fig. 4:.` The same reference characters with a prime mark added have been used in this figure to designate the p-arts which correspond to those of the original embodiment. Referring to Fig. 4, the common bar 43', which is moved by any one of the current responsive control elements 33', forms one side of a movable parallelogram and is hingedly or pivotally connected at its lower end to one end of the ambient temperature compensating element 55l which forms the next adjacent side of the parallelogram. Connecting bar 13 and a; second bimetallic element 80, similar to the element 55', complete the movable parallelogram. The ends forming the corners of the parallelogram are pivotally or hingedly connected together as indicated at 16. The parallelogram pivots on two lcommon rotational points or pivots 82 which are vertically aligned and disposed so that the parts are balanced with respect to these common pivots. The control elements 33 are engageable with collars or projections'53 secured to the bar 43' for moving the bar. A spring 65' biases the movable parallelogram in a counter-clockwise direction to normally maintain the movable contact 53 in closed circuit position. The operation of this modification is brieily'as follows: When any one of the current responsive bimetal elements 33' is deflected downwardly in response to anoverload in its circuit, the bar 43' is moved downwardly thereby causing the element 55 to move clockwise about the pivot 82 and effect opening of the contacts 53'-6I. It will be understood that the entire parallelogram comprising the parts 49',l 55', 18, and 80 is moved Vabout the pivots 82 by the operation of any one of the current responsive bimetal elements 33'.

The ambient temperature compensating element 55' and the bimetal element 80 operate to shift the position of the bar 43' upwardly or downwardly, as the case may be, in response'to An additional inertia body 'I9 may be the balanced construction described above, it Will be readily apparent that any vibra f changes in ambient temperature so as to maintain a fixed distance between the ends of the current responsive bimetal elements 33 and the collars53 on the release bar 49 regardless of changes in ambient temperature.

If complete static balance oi the movable train of elements is not found `to vbe necessary, a degree of balance may be obtained by supporting the 'ambient temperature compensating element 55 at its center of gravity.

A modification of the invention is shown ln Fig. 2. In this modication of the invention the ambient temperature compensating element 55 which is of bimetallic material is biased by the spring 65 so that its left-hand end normally engages and restrains a. releasable latch member 8|. The movable contact 9.3 in this embodiment is carried by a lever 95 which is pivoted on a pin 81 and directly connected with releasable latch member The latch member 9| may foi-m an internal part of the lever-95 if desired.

The cooperating stationary contact 89 which is normally engaged by the movable contact 83 as long as the latch 8| is held in latched posi tion by the element 55 is carried by a resilient conducting strip 9| which provides the contact pressure, The conducting strip 9| is secured to a carrier 93 of conducting material having a projecting portion 95 which engages the pivot' 51 and the adjusting lever 61. The stationary contact 89 is thus electrically connected to the adjusting lever 61 and through the same to the conducting strip 11. The carrier 93 is also provided leased by clockwise movement of the ambient.

temperature compensating lelement 55 upon downward movement of the common actuating bar 49.

The lever 85, movable contact 83 and the latch 8| are re-set to the closed and latched position by means of a manually operable resetting member 99. The resetting member 99 is mounted for horizontal sliding movement 'ai the lower end of the casing 2| and Vis biased to an inoperative position by a spring |0|. T' e resetting member 99 is also provided with .i manualv operating handle |03 by means of which it may be moved to the left against the bias of the spring |0| to effect resetting of the lever 85 to closed latched circuit position after cooling of the bimetal control elements. When the resetting handle is moved to the left to reset the interruptor, the resetting member 99, which is moved by the handle, engages the latch arm 8| and moves this arm and the connected contact arm 85 in a counterclockwise direction 'to -the closed and latched position shown in Fig. 2.

The structure of this embodiment of the invention is identical to that of the original embodiment shown in Fig. 1 and described in connection therewith except for the arrangement and construction of the contacts 83 and 89 and the latch 8|. Hence the same reference charactors have been used in Fig. 2 to designate the corresponding elements and parts Which are identical to those shown in Fig. l.

'I'he operation of the device shown in' Fig. 2 is `briefly as follows. The common bar 49 is moved downwardly by deiiection of any one of the current responsive bimetal control elements 33 in response to predetermined current conditions. This downward movement oi the bar 49 eilects clockwise rotation of the ambient temperature compensating element. 55 bodily about its pivot 51, causing the free end thereof to disengage the latch 8|. As soon as the latch 0| is thus released, the spring 91 moves the lever 05 and cont-act 83 to open circuit position. This eilects deenergization of the electromagnetic operating means 1, causing opening of the contacts 5 of the interrupter in the same manner as previously described in connection with Fig. 1.

To re-set the interrupter following the above described tripping or releasing operation, the resetting member 99 is moved to the left by means of the resetting handle |03 to return the lever I9 and contact 83 to the closed and latched position shown in Fig. 2. The interrupter contacts 5 will then be closed upon energization of the control circuit |1.

The vambient temperature compensating clement 55 functions in substantially the same manner as described in connection with Fig. 1. A change in ambient temperature causes the element 55 to be deiiected up or down, as the case may be, to change the original position of the common bar 49. .A stop on the casing 2| is engageable by the underside of the latch end of the bimetal element 55 to limit movement of this end of the bimetal beyond the latching position shown in Fig. 2.

The current operating characteristics of the device may be adjusted by changing the position of the adjusting lever 61 in the same manner as described for the embodiment shown in Fig. 1. In such instance, the position of the stationary contact I89 must also be adjusted for the new position of the pivot 51. A suitable screw (not shown) is provided to maintain the pivot 51 and the stationary contact carrier in adjusted position.

The movable train of elements taking part in the automatic release in the embodiment shown in Fig. 2 are all statically balanced with respecty to the pivot 51 in the same manner as for the embodiment shown in Fig. 1, that is to say, the common pivot 51 is disposed at the center of gravity of the entire train oi movable elements.

A further modification of the invention is shown in Fig. 3. In this embodiment, an additional inertial body |05 of relatively large mass is provided for preventing false tripping of the breaker by shocks or jarring forces. The inertial body |05 is pivotally mounted at |01 at the center of gravity of the -body |05 and parts carried thereby. A pre-tensioned spring |09 is secured at one end to a projection l of the body |05. 'I'he free end of the spring |09 normally engages a stirrup shaped stop H3 carried by the body |05. The common insulating bar 49 which is actuated by any one of the current responsive birnetal control elements 33 engages the pretension spring |09 at its lower end at a point adjacent the stop H3. v

An ambient temperature compensating element |06, which is of bimetallic material, is secured at its right-hand end to a projection H5 of the inertial body |05. The free end of the ambient temperature compensating element |00 normally engages and restrains the latch portion 0| oi' the contact lever to maintain the movable contalct 03 in engagement with the resiliently supported stationary contact 89 in the same manner asin the embodiment shown in Fig. 2.

A spring ||1 corresponding in function and operation to the spring 95 of the embodiments v previously described, vbiases the body in a .counter-clockwise direction. This spring serves to yleldingly maintain the body |05 and the parts carried thereby in the position shown in Fig. 3, and also acts to return the body |05 to the normal position shown following an automatic releasing operation of the device.

The tension. of the spring |09 is selected of such strength that lfor relatively slow downward motions of the common bar 49, caused by delicotion of any one of the current responsive bimetallic control elements 93, the spring |09remains in engagement with the stop H3 so that the motion of the bar 49 is transferred to the body |05, causing clockwise movement of the body |05 about its pivot |01 to effect release of the latch 9| and consequently automatic opening of the contacts 93, 99 and the interrupter. 'Howeven when the bar 49 is moved quickly, as, for example, by vibrations or jars, the spring |09 fiexes as indicated by the dotted lines to take up the quick movement of the bar 49. The inertial body |05, due to its relatively heavy mass, and the fact4 that it is pivoted at its center of gravity remains stationary during flexing of the spring |09. Thus the accelerating forces produced by vibrations or jars will not cause automatic operation of the device. It will be noted that'the tension spring |09 and the ambient temperature compensating element 55 extend parallel to the surfaces of the inertial body |05, thus providing a compact structure with no objectionably projecting parts.

The current operating adjustment of the'device shown in Fig. 3 may take place in the same manner as in the devices disclosed inn Figs. 1 and 2. 'I'he .lever 85. movable contact 99 and latch 9|' are reset to the closed and latched position by a manually operable resetting means (not shown), which is of the same construction as the resetting means shown in Fig. 2. Y

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details thereof may be made without departing from the spirit oi' the invention. It is desired, therefore, that the appended claims be given the broadest reasonable interpretation permissible in the light of the prior art.

I cla-im as my invention:

l. A circuit interrupter having, in combination, a train oi elements movable to cause automatic opening of the interrupter, a bimetallic control element operable in response tompredetermined conditions to move said train of elements to cause automatic opening of the interrupter and an ambient temperature compensating device arranged in the train of elements and movable therewith. the train of elements being movable about at least one common rotation point and being statically balanced with respect thereto. Y f

2. A circuit interrupter having, in combination, means operable to cause opening of the interrupter, a train of elements including an ambient temperature compensating element movable with `respect to at least one common rotation center to cause said means to effect opening of the interrupter, and a current responsive bimetal con- `trolelement operable v`in response to predetermined conditions to move said train of elements for causing said means to effect said opening of, said contacts, saidhcommon rotation center -ture compensating element movable about a common pivot to cause opening of said contacts,

and a current responsive bimetal control element operable in response to predetermined conditions to bodily move said ambient temperature compensating element to cause said vopening of said contacts, said common piv'ot being disposed substantially at the common center of -gravity of the ambient temperature compensating element and the means movable therewith.

4. In a circuit interrupter, relatively movable contacts, means including an ambient temperature compensating element of bimetallic material pivotally mounted substantially at its center of. gravity and movable about its pivot to cause opening of said contacts, and a current responsive bimetal control element operable in response to predetermined conditions to move said ambient temperature compensating element sponding pole to cause the device to e'ect openabout said pivot to cause said opening of contacts.

5. In a circuit interrupter, relatively movable contacts, means including an ambient temperature compensating element of bimetallic material movable about a common pivot to cause opening of said contacts, a trip member for moving said means and ambient temperature compensating element about said pivot, and one or more current responsive bimetal control elements operable in response to predetermined conditions to move said trip member to cause said means to effect said opening of the contacts, said pivot being located substantially at the common center ofgravity of the ambient temperature compensating element and parts movable therewith.

6. In a circuit interrupter, relatively movable contacts, means including a current responsive bimetal control element operable in response to predeterminedmonditions to cause opening of said contacts, and an ambient temperature compensating element pivotally mounted substantially at its center'ot gravity and moved bodily by said bimetal element in causing said opening of said contacts, said ambient temperature com-` pensating element acting to compensate for movement of said control element by changes in ambient temperature.

7. In -a circuit interrupter, relatively movable contacts, means operable to cause opening of said contacts comprising a current responsive bimetal control element movable in response to predetermined current conditions, and a pivoted ambient temperature compensating element of bimetallic material movable about its pivot by said control element to cause opening of said contacts, said ambienttemperature compensating element being pivotally mounted at a point such that the acceleration forces on said compensating element resulting lfrom vibrations or jars are balanced with respect to the pivot axis of said element.

8'. In a multi-pole circuit interrupter, a device operable to cause automatic opening of, the interrupter comprising a plurality of current responsive bimetal control elements one for each pole of the interrupter each movable in response to predetermined current conditions of its correing of the interrupter, a common bar movable by any one of said control elements in response to said predetermined conditions, and apivoted ambient temperature compensating element oi' bimetallic material engaged by said bar and movable bodily about its pivot by said bar upon movement of any one of said control elementsv in response to said predetermined conditions to cause automatic opening of the interruptor, the pivot o! said ambient temperature compensating element being located at the common center of gravity of said ambient temperature compensating element and parts movable therewith.

9. In a multi-pole circuit interrupter, a device operable to cause automatic opening or the interrupter comprising a plurality of current responsive bimetal control elements one for each pole of the interrupter each movable in response to predetermined current conditions oi' its corresponding pole to cause the device to eil'eot opening o! the interrupter, a common bar movable by any oneoi' said control elements in response to said predetermined conditions, and a pivoted ambient temperature compensating element of bimetallic material engaged by said bar and movable about its pivot by said bar upon movement oi' any one of said control elements in response to said predetermined conditions to cause automatic opening of the interrupter. said ambient temperature compensating element being pivotally mounted at the common center of gravity of said compensating element, said bar, and any parts carried by said element and bar.

10. In a multi-pole circuit interrupter, means including contacts actuatable to cause interruption of the circuit, means operable to actuate said contacts to cause automatic opening of the interrupter comprising a plurality of thermal control devices, each operable in response to predetermined current conditions in its corresponding pole of the interrupter to cause the actuation of said contacts, a common bar movable by any one of said control devices in response to said predetermined conditions, and a single ambient temperature compensating element of bimetallic material movable by said bar to cause the actuation otlsaid contacts upon movement of any one of said control devices in response to said predetermined current conditions, said bar and said compensating element being movable about a common rotational point located substantially at the common center of gravity oi' said bar and said compensating element and parts movable therewith.

l1. In a circuit interrupter, means comprising a train o! elements having at least one common rotational point and movable one by the other to cause opening of the interrupter, one or more current responsive bimetal control elements operable in response to predetermined current conditions to move said train of elements to cause opening of the interrupter, an ambient temperature compensating element arranged in the train of elements and movable therewith in causing opening of the interrupter, said train of elements being balanced with respect to said common ri tational point or points.

12. In a circuit interrupter, means operable to cause opening of the interrupter comprising a bimetal ambient temperature compensating element rotatably mounted about a point between its ends and movable about said rotational point by said means to cause opening of the interrupter, a common bar connected to said ambient temperature compensating element for moving said element about said rotational point, and one or more current responsive bimetal control elements each operable in response to predetermined `current conditions to move said bar and thus move said ambient temperature compensating element to effect opening of the interrupter, said ambient temperature compensating element being rotatably mounted with its rotational point at the common center of gravity o1' said ambient temperature compensating element, said common bar, and any parts connected to said element and bar. i

13. In a circuit interrupter, means operable to cause opening of the interrupter comprising a rotatably mounted inertial body of relatively heavy mass. a tension spring on said body, a common bar engaging said spring for partially rotating said body when said bar is moved relatively slowly, an ambient temperature compensating element carried by said body and movable therewith, and one or more current responsive bimetal control elements each operable in response to predetermined current conditions to move said bar relatively slowly for causing partial rotation of said body to eiiect said opening oi the interrupter, said inertial body being rotatably mounted with its axis of rotation at the common center of gravity of said body and the elements carried thereby and connected thereto,

said tension spring being ilexed by quick move-A tively slowly, an ambient temperature compensating element carried by said body and movable therewith, said tension spring and said ambient temperature compensating element extending parallel to the surfaces of said body, and one or more current responsive bimetal control elements each operable in responsev to predetermined current conditions to move said bar relatively slowly for causing partial rotation o! said body to eiect said opening of the interrupter, said inertial body being rotatably mounted with its axis oi' rotation at the common center of gravity of said body and the elements carried thereby and connected thereto, said tension spring being flexed by quick movements of said bar in response to vibrations and jars to prevent movement of said body in response to vibrations and jars.

15. In a circuit interrupter, means operable to cause opening oi' the interrupter comprising a bimetal ambient temperature compensating element pivotally mounted intermediate its ends and movable bodily about its pivot by said means to cause opening oi' the interrupter, a common bar connected to said element for movingsaid element about its pivot, one or more current responsive bimetal control elements each operable in response to predetermined conditions to move said bar and thus movev said ambient tempera-` ture compensating element about its pivot to effect opening oi' the interrupter, and adjusting means for moving the pivot support oi' said ambient temperature compensating element to vary the current-operating point of said control elements.

o'r'ro mmm. 

